Feat/ruby to typescript 3

[michaelmalave]

Summary

This PR finishes the migration to a TypeScript-only repo: the Ruby devcenter gem, bin/devcenter, and lib/** are removed. The supported interface is heroku plugins:install @heroku-cli/heroku-cli-plugin-devcenter and heroku devcenter:*.

• Breaking: Users must stop using gem install devcenter / the devcenter binary and use the Heroku CLI plugin instead.
• Coverage: Adds .c8rc.json and runs c8 --all --check-coverage in npm test with 80% thresholds on src/**/*.ts (then Mocha and ESLint).
• Tests: Adds shared-lib unit tests (article parsing/split, Dev Center client, paths, netrc auth, preview templates, package export).
• Repo: .gitignore trimmed for Node/TS; Dependabot drops Bundler, adds github-actions + npm (with existing npm grouping/ignores).
• Inventory: Adds .heroku/components-inventory/devcenter-cli.json for the components sync workflow.
• Docs: README and CONTRIBUTING updated for plugin-first usage, Node 22+, and test/coverage behavior.

Type of change

Type of Change

Breaking Changes (major semver update)

• Add a ! after your change type to denote a change that breaks current behavior

Feature Additions (minor semver update)

• feat: Introduces a new feature to the codebase

Patch Updates (patch semver update)

• fix: Bug fix
• deps: Dependency upgrade
• revert: Revert a previous commit
• chore: Change that does not affect production code
• refactor: Refactoring existing code without changing behavior
• test: Add/update/remove tests

Testing

Setup:

npm install
npm run build
heroku plugins:link .

Run of commands

heroku devcenter --help
heroku devcenter:open --help
heroku devcenter:pull --help
heroku devcenter:push --help
heroku devcenter:preview --help

Related Issues

GitHub issue: #[GitHub issue number]
GUS work item: W-20867948